With the latest development of the nanotechnologies, high sensitivity, high specificity, and high selectivity of nano-materials such as nano-particles, nano-wires and nano-devices have been applied to various fields. Among the various nano-materials, graphene has been recently subject to researches in view of its superior electrical, physical, and optical properties. In graphene, in which carbon atoms form a hexagonal structure, each carbon atom is bonded to its peripheral atoms through a strong covalent bond, and as one carbon atom has one non-bonded electron, the electrons easily move in a two-dimensional structure within the graphene, so that the graphene has a current density of about 108 A/cm2, which is about 100 times greater than that of a copper per unit area at a room temperature. In addition, the mechanical strength of the graphene is about 200 or more times stronger than that of steel, and since the flexibility of the graphene is also excellent, the graphene does not lose its electrical conductivity even when it is stretched or folded, so that the graphene can be applied to a flexible display, a wearable display or others. However, the graphene has a disadvantage in view of application thereof because aggregation occurs among graphenes, and thereby, significantly deteriorating a degree of dispersion in a common solvent.
As one of measures to overcome this disadvantage, a small nano-sized graphene quantum dot method has been researched and developed over recent years. Graphene quantum dot compound is a zero (0)-dimensional material having a size of a few nanometers to tens of nanometers, and since the compound is easily dispersed in various organic solvents and has a property of light emission over various ranges, it can be applied to bio-imaging research, light emitting devices, photoelectronic devices or others.
Korean Patent Application Publication No. 10-2012-0029332 relates to graphene quantum dot light emitting device and a fabricating method thereof. Most of conventionally reported methods for synthesizing graphene quantum dot use graphene oxide as a starting material. This method is disadvantageous in that the synthesis process is complicated, and a yield rate of the graphene quantum dot is quite low. In addition, relevant experiments are carried out under a strong acidic condition, and since a large amount of salt is added for neutralization during a purification process, the process becomes complicated. Further, since a toxic compound is used as an oxidant, it may cause environmental pollution.